1. Field of the Invention
The present invention relates to a method for forming a thin film for a semiconductor device. More particularly, the present invention relates to a method for forming a ternary silicon boron nitride (SiBN) thin film having a low dielectric constant using an atomic layer deposition (ALD) process.
2. Description of the Related Art
Conventionally, a silicon nitride layer (SiNx) has been widely used in the manufacturing of semiconductor devices for several reasons. First, a SiNx layer has a high etching selectivity over a silicon oxide layer in a reactive ion etching (RIE) process and a wet etching process. Second, a SiNx layer exhibits strong oxidation and abrasion resistances. Third, a SiNx layer has an excellent diffusion barrier characteristic. However, a SiNx layer has a high dielectric constant of about 7. This high dielectric constant causes a propagation delay since parasitic capacitance increases as a chip size is reduced.
Recently, in view of the above disadvantage of a SiNx layer, the SiNx layer has been replaced with a boron nitride (BN) layer having a relatively low dielectric constant as a dielectric layer for a semiconductor device. The BN layer is formed by an ALD process at a low temperature in a range of 200xc2x0 C. to 550xc2x0 C., so that a conformal BN layer is formed.
The BN layer formed using the ALD process has a low dielectric constant, between 2.2 and 5 depending on deposition conditions, thereby reducing the propagation delay in comparison with a SiNx layer having a dielectric constant of about 7.
However, an ALD BN layer has several disadvantages. For example, an ALD BN layer is easily hydrolyzed by moisture in the atmosphere, is wet etched by a high temperature wet chemical based on sulfuric acid H2SO4, and has poor oxidation resistance.
Further, a conventional SiBN layer formed by a plasma enhanced chemical vapor deposition (PECVD) process has poor step coverage.
In an effort to overcome the problems described above, it is a feature of an embodiment of the present invention to provide a method for forming a SiBN thin film having excellent step coverage and uniformity in thickness over an entire surface of a wafer using an atomic layer deposition (ALD) process.
It is another feature of an embodiment of the present invention to provide a method for forming a SiBN thin film having a low dielectric constant and a low etching rate over a high temperature wet chemical.
It is yet another feature of an embodiment of the present invention to provide a method for forming a SiBN thin film having an excellent reactive ion etching (RIE) characteristic.
In accordance with one aspect of the present invention, there is provided a method for forming a thin film for a semiconductor device using an atomic layer deposition process, including supplying a first reactive material and a second reactive material to a chamber having a wafer therein, thereby adsorbing the first reactive material and the second reactive material on a surface of the wafer, supplying a first gas to the chamber, thereby purging the first reactive material and the second reactive material that remain unreacted, supplying a third reactive material to the chamber, thereby causing a reaction between the first and second reactive materials and the third reactive material to form a monolayer of the thin film, supplying a second gas to the chamber, thereby purging the third reactive material that remains unreacted and a byproduct, and repeating the above steps for forming the monolayer of the thin film a predetermined number of times to form a ternary thin film having a desired thickness on the wafer.
Preferably, the ternary thin film is a SiBN thin film. The first reactive material preferably includes BCl3, BBr3, B2H6 or BF3 gas and is supplied at a gas flow rate of 50 sccm. The second reactive material preferably includes SiH2Cl2, SiCl4, Si2Cl6 or SiH4 gas and is supplied at a gas flow rate of 60 sccm. Preferably, the first and second gases are an inert gas or N2 gas. The first and second gases may be supplied at a same or different rate, and are preferably supplied into the chamber at a flow rate of about 750 sccm. The third reactive material is preferably one of NH3 gas or N2H2 gas. As the third reactive material, NH3 gas or, alternatively, a mixture of N2 gas and H2 gas is converted into free radicals by application of plasma, and then the free radicals along with any remaining gases, if any, are used as the third reactive material. The third reactive material is preferably supplied at a gas flow rate of 500 sccm. The third reactive material may be converted to plasma in the chamber using an inductive coupled plasma (ICP) generation process, a direct current (DC) plasma generation process, a radio frequency (RF) plasma generation process or a microwave plasma generation process to increase a reaction rate between the first and second reactive materials and the third reactive material. The wafer is preferably heated to a temperature in a range of about 400xc2x0 C. to 600xc2x0 C. and the chamber maintains an internal pressure in a range of about 1 to 3 torr.